Year	Percent
1990	30.63528
1991	26.28417
1992	22.95589
1993	28.03705
1994	33.89577
1995	35.64549
1996	30.33082
1997	30.96658
1998	35.17556
1999	34.72542
2000	29.97238
2001	32.07574
2002	36.43327
2003	37.75795
2004	39.60089
2005	42.43027
2006	43.37747
2007	45.5407
2008	45.80878
2009	49.89775
2010	49.3385
2011	47.86536
2012	51.03908
2013	49.63326
2014	50.61194
2015	52.14983
2016	50.14832
2017	50.38068